1. Field of the Invention
The invention concerns a method for placing on standby an oven for heat-treating thermoplastic material preforms.
The invention more particularly concerns a method for placing an oven for heat-treating thermoplastic material preforms on standby during a temporary cessation of production, the oven including:                a device for conveying preforms that moves the preforms through the oven;        at least one heating lamp that is adapted to emit infrared radiation when it is switched on, each storage element being disposed along the route of the preforms;        at least one heat-storage element that is made from a material having a high thermal capacity, the storage element being adapted to be heated by the heating lamp;        an electronic unit for controlling the heating lamps.        
2. Description of the Related Art
The manufacture of thermoplastic material containers, such as large or small bottles, etc., is generally effected on the basis of preforms, sometimes called blanks, which are introduced into a molding device with which are associated blowing or drawing-blowing means.
Before they are molded by blowing or drawing-blowing, the preforms are heated in a heat-treatment oven so as to confer on them a structure sufficiently malleable for the blowing operation.
Installations for mass production of such containers are equipped with treatment ovens including a heating tunnel provided with means for heating the preforms. The preforms are generally transported through the heating tunnel at high speed without stopping. The tunnel has a length sufficient to enable heating of the preforms as they pass through.
The preform heating means are generally formed by heating lamps that emit infrared radiation. These lamps traditionally take the form of horizontal tubes that are disposed on a wall of the heating tunnel. Each tunnel section is equipped with a plurality of lamps, which are stacked in order to effect appropriate heating of the whole of the body of the preform.
The wall facing the heating lamps is equipped with ventilation means for agitating the air in order to prevent some areas of the preforms from being overheated by the infrared radiation.
In order for all of the infrared radiation to be used for heating the preform, reflectors are disposed behind the lamps in order to reflect the infrared rays in the direction of the preforms.
Some operating incidents make it obligatory to interrupt production by the installation temporarily. In this case, the oven is no longer fed with preforms. The preforms present in the oven at the time feeding is interrupted finish their travel normally and then exit the oven in the direction of the blowing device. When the last preform is evacuated, the oven no longer contains any preforms.
Some vulnerable parts of the oven are liable to be damaged by a high temperature. These vulnerable parts risk being damaged if the heating lamps remain switched on with no preforms passing through.
Furthermore, it is also preferable for the interior of the oven to be maintained at a temperature sufficient for production to be restarted rapidly, avoiding a long step of restoring the oven temperature.
The oven emptied in this way is then placed on standby. It is known to employ a method of placing the oven on standby during which the intensity of the heating lamps is lowered in order to prevent the vulnerable parts of the oven being overheated and therefore damaged. The ventilation means are furthermore activated in order to evacuate the air heated by the lamps and to cool the vulnerable parts of the oven more effectively.
Such a method consumes a great deal of energy, however. The invention therefore proposes a putting on standby method enabling the consumption of energy to be reduced at the same time as ensuring optimum operation of the treatment oven.